Dielectric die

ABSTRACT

1,130,615. Dielectric heating electrodes. FORD MOTOR CO. Ltd. 24 Aug., 1966 [20 Oct., 1965], No. 37882/66. Heading H5H. [Also in Division B5] A die for bonding together selected areas of sheets 21, 23, 25, 27 of dielectric material comprises an electrode assembly which includes a plurality of electrodes 43, 45, 47 electrically connected in parallel to a source 73 of R.F. current, the electrodes 43, 45, 47 having working surfaces 43-1, 45-1, 47-1 to press the selected areas against another electrode 31 connected to the source 73 to bond the areas by dielectric heating, the electrical conductivity of the electrodes 43, 45, 47 differing from one electrode to another. A door panel 10, Fig. 3, for an automobile comprises a press wood board 21, a pad 23 comprising rayon fibres and a thermoplastic resin, a thermoplastic vinyl sheet 25, e.g. polyvinyl chloride, and a second thermoplastic vinyl sheet 27. The electrodes 43, 45, 47 are electrically connected to a lower electrode 33 which is connected to the source 73. The electrodes 31, 33 are made of aluminium, the electrode 43 of copper, the electrode 45 of brass, stainless steel or another alloy and the electrode 47 of copper or an alloy. In one embodiment, the electrodes 43, 47 have the same electrical resistivity and the electrode 45 has a greater resistivity. In a second embodiment, the electrode 47 has a greater resistivity than the electrode 43 but less than the electrode 45. In operation, the sheets 21, 23, 25, 27 are placed on the electrodes 43, 45, 47 and polyurethane spacer pads 49, 51, 53, 55 and held in position by clamps 39, 41. Stays 37 are disengaged and the electrode 31 is closed to overlie the sheets. The electrodes 31, 33 are forced together by pressure applied pneumatically or hydraulically and then R.F. is supplied to effect bonding.

Sept. l0, 1968 J. c. KIM 3,401,248 j DIELECTRIC DIE Filed Oct.` 20, 1965 HIGH FREQUENCY osclLLAToR FIGB ,3o JOHN u KIM /71 31 43-1 /10 45-1 auf 47-1 i /Nvf/vron 4s 4.a .f1 v4J .s3 .53' ATTORNEYS United States Patent() 3,401,248 v DIELECTRIC DIE John C. Kim, Pontiac, Mich., assignor to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Filed Oct. 20, 1965, Ser. No. 498,713 7 Claims. (Cl.l 219-,10.53)

ABSTRACT or THE DISCLOSURE A method and a device for bonding dielectric materials are disclosed. Each is characterized by the utilization of electrodes of varying size and inversely varying electrical resistivity to provide controlled heating.

Summary of the disclosure Method and apparatus for bonding together dielectric materials by producing varying amounts of heat at spaced apart locations within a dielectric lamination from a single-source, power input, said method comprising sandwiching said dielectric lamination between a platen electrode and a pair of design electrodes and controlling the heat generated |between said platen electrode and said design electrodes by varying the electrical resistivity of said design electrodes inversely with the work face areas of the same, said apparatus'comprising a source of high frequency oscillatory energy, a first die member including a platen electrode in electrical connection with said source, a second die member including `a plurality of bonding design electrodes in electrical connection with said power source, and means for urging said first die member and said second die member together when said dielectric materials are sandwiched therebetween, Said design electrodes including rst'design electrode having a'working face of predetermined area and formed of metal having a predetermined electrical resistivity and a second design electrode having a work face of significantly lesser area than said predetermined area and formed of metal having an electrical resistivity significantly greater than said predetermined electrical resistivity.

This invention is concerned with the field ofdielectric heating and is particularly directed to a method of and means for sealing, embossing, and/or scoring super-imposed sheets of flexible plastic material by meansof high frequency currents and pressure. More particularly, this invention relates to an improved electrode die capable of producing varying amounts of heat at spaced apart locations within a dielectric lamination from a single source, power input.

:It is well known in the art thatl there area number of synthetic resins which become soft in the presence of suiciently high temperature and which may thus be bonded together by the application ofdielectric heating. These materials are generally classed as thermoplastics and include a Ivast number of commercially available materials which are useful in the fabrication of upholstery,' fabrication of waterproof coverings, air-tight enclosures and packages for the shipment of foods, chemicals or other materials which deteriorate in the presence of air or moisture.

Dielectric heating is a selective heating process whereby heat can be developed within an electrically insulating or dielectric material from the frictional heating caused by molecular rotation within the dielectric by an alternating current of radio frequency. i

The instant die has general utility wherever trim materials are employed including, but not by way of limitation, the production of interior trim for automotive vehicles. There is an increasing--demand'to provide trim sheets or panels having decorative designs. Such panels decorative ice conventionally include a trim material, e.g. one or v,more vinyl sheet materials, positioned on a fibrous or foam pad which is made of or 4impregnated with a heat fusible resinous material and is supported on a iberboard. Upon operation of the dielectric press, an embossed pattern is produced wherein the trim-material is bonded to the backing through the pad, the resin in the pad along the embossed lines having been melted andcured, thus serving as a bonding adhesive. In automotive soft trim Ymanufacturing, the dielectric dies are constructed according to a given soft trim component design such 4as a door panel or seat bolster. These individual designs require that a die have many different types of bondingl bars or design electrodes in their construction. As the areas to be bonded increases, the amount of power required to produce .the heat necessary for satisfactory bonding also increases;

In a method and/ or apparatus suitable for use in conjunction With an assembly line, simplicity of `design and operation are advantageous, if not a requirement, as i's adaptability to rapid and frequent modification.

It is one object of this invention to provide an irnproved method and apparatus for fast efficient dielectric heating.

It is another object to provide an improved method and apparatus adapted to meet varying heat requirements within a single die press without increasing power input or employing multiple circuitry by employing bonding design electrodes of varying mass and work face area electrically connected in parallel and formed of different metals, the electrical resistivity of such metals varying inversely with the work face area of the same.

These and other objects and advantages of this invention will be readily apparent from the following detailed description of a preferred embodiment thereof and the accompanying drawings, in which:

FIGURE l is a perspective view of an upholstered door panel for an automobile illustrating an embossed design made in accordance with this invention and indicating areas of bonding to be effected using the die illustrated in the succeeding figures;

FIGUR-E 2 is a perspective view of a die assembly in accordance with this invention; and

FIGURE 3 is a cross-sectional view taken along line 3 3 of FIGURE 2.

Referring now to the drawing, there is shown in FIG- URE la door panel 10 upon which three separate em'- bossed areas 13, 15 and 17 indicate three areas of dielectric bonding hereinafter further described in relation to FIGURES 2 and 3. A portion of door panel 10 is shown in cross section in FIGURE 3 priorto Ibonding and comprises a pressed wood board 21, a pad 23- comprising viscose bers and a suitable thermoplastic resin,a first thermoplastic vinyl sheet 25, e.g. polyvinylchloride, and a second thermoplastic vinyl sheet 27 which may be of the same chemical composition as sheet 25.

Referring now to FIGURES 2 and 3, there is shown a die assembly 30 comprising an upper platen electrode 31, lower platen electrode 33, hinge means 35, stop means 37 for holding the die open for loading, clamping means 39 and 41 for holding the panel components in place, bonding design electrodes 43, 45 and 47, and polyurethane spacer pads 49, 51, 53 and 55. In FIGURE 2 the spacer pads are removed from areas 61 and 63 to better show the bonding design electrodes. In this embodiment, electrodes 31 and 33 are aluminum, electrode 43 is copper, electrode 45 is brass, stainless steel, inconel or other suitable alloy and electrode 47 is copper or a suitable alloy. In one embodiment, electrode 47 has the same electrical resistivity as electrode 43 and electrode 45 has a greater resistivity. In a secondembodiment,

electrode 47 has a greater electrical resistivity than electrode 43 but a lesser electrical resistivity than electrode 45. Electrodes 43, 45 and 47 are all in electrical connection with electrode 33.

Electrodes 31 and 33 are electrically connected to a high frequency oscillator 73 or other means for providing a high frequency alternating electric current via conductors 71 and 75 respectively. Oscillator 73 is, of course, connected to a suitable electric power source, not shown. For instance, with dielectric presses rated at about 30 to about 100 kilowatts, the oscillatory has been connected with a 44o-volt AC circuit through conventional conversion devices such as rectifers, transformers, etc., to provide aV direct current to the oscillator -at about 12,000 D C. volts. This is then converted by the oscillator to about 5,000 R.F. (radio frequency) volts at about 10 to about 30 megacycles per second. These figures are merely exemplary as considerable variance in operating conditions is disclosed in the literature. For example, U.S. Patent 3,053,960 discloses the use of a frequency range from 2 to 200 megacycles per second. v

In operation the components of panel are placed in the indicated order over the design electrodes 43, 45 and 47 and spacer pads 49, 51, 53 and 55 and held in position by clamping means 39 and 41 while electrode 31 is held in open position by stop means 37. Stop means 37 is removed or disengaged permitting electrode 31 to close over the clamped panel components and pressure is applied by pressure means, not shown, so as to force electrodes 31 and 33 closer together. The requisite pressure for bonding and/or embossing is thus provided, e.g. 200-300 pounds per each square inch of bonding area. In practice this will ordinarily be effected by pneumatic or hydraulic means. When the panel components are under the desired pressure, a high frequency alternating current is applied through the aforedescribed circuit to the electrodes 31, 33, 43, 45 and 47 with resultant heating and bonding of the thermoplastic materials in the areas directly between the design electrodes 43, 45 and 47 and the platen electrode 31.

In the dies of this invention, the amount of heat required at a given site is controlled in a single circuit by varying the electrical resistivity of the design electrodes which are electrically connected in parallel in accordance with their mass and/or work face area. The electrodes 43, 45 and 47 each have a working face 43-1, 454 and 47-1 which is brought into contact with at least one of the dielectric components of the panel, or other workpiece, when the ldie is in use. Within a group of design electrodes, thus electrically connected, the heating properties of at least two such electrodes are controlled in relation to each other by varying their electrical resistivities inversely with their work face areas. This is effected through a proper choice of electrode metals. Thus, when a uniform amount of power is applied to the die circuit, those areas requiring predetermined amounts of heat receive the requisite amount from electrodes in the same circuit.

Although the detailed description has been primarily confined to a particular embodiment, it will be understood that other embodiments and modifications may be used within the scope of the invention as set forth in the appended claims.

Iclaim:

1. A die suitable for bonding together dielectric materials comprising a first conductor for electrical connection with a source of high frequency oscillatory energy, a second conductor for electrical connection with said source of energy, a first die member including a platen electrode electrically connected to said first conductor, a second die member including a plurality of bonding design electrodes spaced apart and electrically connected in parallel by said second conductor, said design electrodes each having a work face, and means for urging together said first die member and said second die member when said dielectric materials are sandwiched therebetween in a manner'such as'to bring the work faces of said design electrodes into contact withat least one of said dielectric materials, said design electrodes including a first design electrode having a work face of predetermined area and formed of metal having a predetermined electrical resistivity'l and a seconddesign electrode having awork face of significantly lesser area than said predetermined area and'formed of metal having an electrical resistivity significantly greater than said predetermined electrical resistivity.

2. A die suitable for bonding together dielectric materials, at least one of which includes a heat softenable resin, comprising a first conductor for electrical connection with a source of high frequency oscillatory energy, a second conductor for electrical connection with said source of energy, a first die member including a platen electrode electrically connected to said first conductor, a second die member including a second platen `supporting a plurality of bonding design electrodes spaced apart and electrically connected in parallel by said second conductor, said design electrodes each having a work face, and means for urging together said first die member and said second die member when said dielectric materials are sandwiched therebetween in a manner such as to bring the work faces of said design electrodes into contact with at least one of said dielectric materials, said design electrodes including a first design electrode having a work face of predeter-4 mined area and formed of metal having a predetermined electrical resistivity and a second design electrode having a work face of significantly lesser area than said predetermined area and formed of metal having an electrical resistivity significantly greater than said predetermined electric al resistivity.

3. A die suitable for embossing and bonding together dielectric materials at least one of which includes a heat softenable resin comprising a first conductor for electrical connection with a source of high frequency oscillatory energy, a second conductor for electrical connection with said source of energy, a `first die member including a platen electrode electrically connected to said first conductor, -a second die member including a second platen electrode electrically connected to said second conductor, a plurality of bonding design electrodes spaced apart, mounted on, supported by, land electrically connected in parallel by said second platen electrode, said design electrodes each having a work face, and means for urging together said first die member and said second die member when said dielectric materials are sandwiched therebetween in a manner such as to bring the work faces of said design electrodes into contact with lat least one 0f said heat softenable materials, said design electrodes including a first design electrode having a work face of predetermined area and formed of metal having a predetermined electrical resistivity and a second design electrode having a work face of significantly lesser area than said predetermined area and formed of metal having an electrical resistivity significantly greater than said predetermined electrical resistivity.

4. A die suitable for bonding together dielectric materials comprising a rst conductor for electrical connection with a source of high frequency oscillatory energy, a second conductor for electrical connection with said source of energy, a first die member including a platen electrode electrically connected to said first conductor, -a second die member including a plurality of bonding design electrodes spaced apart and electrically connected in parallel by said second conductor, said design electrodes each having a work face, and means for urging together said first die member and said second die member when said dielectric materials are sandwiched therebetween in a manner suchas to bring the work faces of said design electrodes into contact with atleast one of said dielectric materials, said design electrodes including a first design electrode consisting essentially of copper and having a work face of predetermined area, and a second electrode having a work face of signicantly lesser area than said predetermined area and formed of metal having an electrical resistivity significantly greater than copper.

5. A die suitable for bonding together dielectric materials comprising a lirst die member, a second die member, and generator means for passing a high frequency alternating current between said members, said first die member comprising a platen electrode electrically connected to said generator means, said second die member comprising a plurality of bonding design electrodes spaced apart, electrically connected in parallel, and electrically connected to said generator means, said design electrodes each having a work face, and power means for urging one of said die members toward the other when said dielectric materials are sandwiched therebetween in a manner such as to bring the work faces of said design electrodes into contact with at least one of said dielectric materials, said design electrodes including a lirst design electrode having a work face of predetermined area and formed of metal having a predetermined electrical resistivity, and a second design electrode having a work face of signicantly lesser area than said predetermined area and formed of rnetal having an electrical resistivity significantly greater than said predetermined electrical resistivity.

6. A die suitable for embossing and bonding together dielectric materials at least one which includes a heat softenable resin comprising a rst die member, a second die member, and oscillatory means for passing a radio frequency alternating current between said members, said lrst die member comprising a platen electrode electrically connected to said oscillatory means, said second die member comprising an electrode support member supporting a plurality of bonding design electrodes spaced apart, electrically connected in parallel, and electrically connected to said oscillatory means, said design electrodes each having `a work face, and power means for urging one of said die members toward the other when said dielectric materials are sandwiched therebetween in a manner such as to bring the Work faces of said design electrodes into Contact with at least one of said dielectric materials, said design electrodes including a lirst design electrode having a work face of predetermined area and consisting essentially of copper, a second design electrode having a work face of significantly lesser area thanl said predetermined area and consisting essentially of brass, and a third design electrode having a work face of signicantly lesser area than the work face of said second design electrode and formed of a metal having an electrical resistivity signilicantliy greater than the brass of said second electrode.

7. In a process for bonding together dielectric materials which comprises positioning said dielectric materials between a platen electrode electrically connected to a source of high frequency oscillatory energy and plurality of spaced apart bonding design electrodes having different work face areas electrically connected in parallel with each other and in series with said platen electrode, applying sutcient pressure to said electrodes to compress said dielectric materials between said platen electrodes and said design electrodes, and dielectrically heating said dielectric materials in the regions directly between said design electrodes and said platen electrode by impressing a high frequency alternating current potential between said platen electrode and said design electrodes, the improvement which comprises controlling the heat generated between said platen electrode and each of said design elect-rodes by varying the electrical resistivity of said design electrodes inversely with the work face areas of the same.

References Cited UNITED STATES PATENTS 7/1962 Beck et al 156-273 X 9/1962 Spieles 2l9-l0.53 

